077
FXUS65 KBYZ 210149
AFDBYZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BILLINGS MT
749 PM MDT WED MAY 20 2026
KEY MESSAGES
- TRANSITION TO COOLER WIDESPREAD RAIN TONIGHT THROUGH THURSDAY.
- MODERATE TO HEAVY SNOWFALL ON NORTH FACING SLOPES OF HIGH
COUNTRY (MAINLY ABOVE 7000 FT) TONIGHT THROUGH THURSDAY. THE
OPENING OF THE BEARTOOTH HIGHWAY ON FRIDAY MAY BE IMPACTED.
- OVER A HALF INCH OF PRECIP IS EXPECTED ALONG SOUTHERN MOUNTAINS
AND FOOTHILLS (>75% CHANCE).
- WARMING TREND FRIDAY THROUGH EARLY NEXT WEEK.
UPDATE
SATELLITE IMAGERY SHOWS AN UPPER LOW OVER SOUTHERN AB WHILE
MESOANALYSIS HAS A 110KT H3 JET DIVING INTO NORTHERN ID. OVER THE
LAST SEVERAL HOURS WE HAVE SEEN SHOWER ACTIVITY INCREASE AS THE
LARGE SCALE ASCENT INCREASES BEHIND A LATE AFTERNOON FRONTAL
PASSAGE THAT HAS SHIFTED WINDS TO NORTHERLY. KBLX VAD WINDS SHOW
NNE WINDS TO NEAR 11KFT MSL, AND APPROPRIATELY WE ARE SEEING AREAS
OF SHOWERS (W/ VERY LITTLE LIGHTNING) INTENSIFY NEAR AND WEST OF
BILLINGS. ENERGY DROPPING OUT OF CANADA WILL PUSH THRU WESTERN MT
INTO WY OVER THE NEXT 24HRS, A FAVORABLE TRACK FOR UPSLOPE PRECIP
INITIALLY OVER OUR WEST THEN SPREADING EASTWARD, WITH HEAVIEST
AMOUNTS IN SOUTHERN UPSLOPE AREAS (I.E. NORTH ASPECTS). STILL
LOOKING FOR AN EASTWARD PROPAGATING AXIS OF MID LEVEL
FRONTOGENESIS THAT SHOULD BE A FOCUS FOR HEAVIEST PRECIP AS IT
PASSES.
FORECAST IS ON TRACK FOR A PERIOD OF RAIN OVER MUCH OF
THE REGION TONIGHT AND THURSDAY. HAVE ADJUSTED POPS/WX PER CURRENT
CONDITIONS AND HIGHER CONFIDENCE. COUPLE ITEMS TO WATCH. FIRST IS
HOW LOW SNOW LEVELS WILL FALL. ALL INDICATIONS ARE FOR SNOW DOWN
TO ~6KFT MSL BY EARLY TOMORROW, AND THIS IS CONSISTENT WITH WHAT
MESOANALYSIS IS SHOWING UPSTREAM, BUT PERHAPS DYNAMIC COOLING CAN
ALLOW A BRIEF CHANGE OVER TO WET SNOW A BIT LOWER THAN THAT.
THE HIGHER ELEVATIONS JUST SOUTH OF RED LODGE AND NEAR STORY MAY
SEE WET SNOW W/O ACCUMULATION. SECOND IS T-STORM POTENTIAL IN THE
EAST AS SURFACE TROF WILL STILL BE NEAR THE MT/DAKOTAS BORDER AT
MIDDAY THURSDAY. THERE IS AMPLE SPREAD HERE, BUT SOME HIGH RES
MODELS SHOW HEALTHY CONVECTION DEVELOPING AND LIFTING THRU OUR FAR
EAST IN THE AFTERNOON...THOUGH GREATER INSTABILITY OVERALL IS
EXPECTED TO REMAIN IN THE WESTERN DAKOTAS. NONETHELESS THIS IS
SOMETHING TO MONITOR AND HAVE RAISED POPS/QPF A BIT IN OUR FAR
EAST TOMORROW. INGREDIENTS SHOULDN'T SUPPORT SEVERE STORMS, BUT
SMALL HAIL AND LOCAL DOWNPOURS ARE POSSIBLE (PWATS UP TO 0.75").
JKL
DISCUSSION
NEXT 7 DAYS (THROUGH NEXT TUESDAY)...
WATER VAPOR IMAGERY SHOWS VIGOROUS SHORTWAVE TROUGH DROPPING SOUTH
FROM ALBERTA INTO MONTANA. ASSOCIATED COLD FRONT IS EXPECTED TO
PUSH INTO EAST CENTRAL MT AROUND 3 PM, AND SLIDE SOUTH THROUGH OUR
CWA LATE TODAY THROUGH THIS EVENING. SCATTERED SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE LATE TODAY.
LATEST MESO-ANALYSIS SHOWS MUCAPE ON THE ORDER OF 100-350 J/KG
LATE TODAY WITH SKINNY CAPE SOUNDING PROFILES. THIS SUGGESTS
GARDEN-VARIETY THUNDERSTORMS WITH ERRATIC WIND GUSTS 25-35 MPH
AND BRIEF DOWNPOURS. CANNOT RULE OUT SOME PEA SIZE HAIL HERE AND
THERE DUE TO RELATIVELY LOW FREEZING LEVELS. HEADS UP TO THOSE
WITH OUTDOOR PLANS THIS EVENING.
AS MAIN ENERGY IN UPPER TROUGH DIGS THROUGH WESTERN MT AND ID, A
COOLER AIR MASS AND UPSLOPE FLOW SETTLES IN OVER OUR AREA TONIGHT.
SO LOOK FOR THE CONVECTIVE PRECIPITATION TO TRANSITION TO A
WIDESPREAD STRATIFORM PRECIPITATION EVENT OVERNIGHT. CROSS
SECTIONS SHOW UPSLOPE DEEPENS TO 600 MB BY 12Z THURSDAY OVER
SOUTH CENTRAL AND FOOTHILL LOCATIONS. THUS, PRECIP WILL BECOME
MOST WIDESPREAD OVER OUR SOUTHERN UPSLOPE AREAS, GRADUALLY
SHIFTING EASTWARD THURSDAY WITH THE UPPER TROUGH AXIS.
THE CHANCE OF AT LEAST 0.50" OF RAIN ARE HIGH IN THESE UPSLOPE
AREAS (>80%) BUT EVEN BILLINGS-HARDIN COULD SEE A HALF INCH (>50%
CHANCE). OTHER AREAS NORTH AND EAST OF I-90 WILL SEE LESS PRECIP
(0.05-0.25"). SOME HI-RESOLUTION MODELS ARE STRETCHING BETTER
PRECIP TOTALS NORTHWARD ALONG THE PIVOTING AXIS OF THE UPPER
TROUGH (THINK EASTERN YELLOWSTONE INTO TREASURE AND NORTHERN
ROSEBUD), SO WOULD NOT BE SURPRISED TO SEE OUR NBM GUIDANCE TREND
THIS WAY. DUE TO DEEP UPSLOPE AND ADDITIONAL DYNAMIC FORCING AS
AFOREMENTIONED TROUGH AXIS PIVOTS AROUND OUR REGION THURSDAY, SOME
AREAS COULD POTENTIALLY SEE OVER AN INCH OF PRECIPITATION. THIS
LOOKS MOST LIKELY ON THE NORTH ASPECTS OF THE
BEARTOOTHS/PRYORS/NORTHERN BIGHORNS INTO SOUTHERN YELLOWSTONE/BIG
HORN COUNTY (20-35% CHANCE).
SNOWFALL...SNOW LEVELS WILL START OUT OVER 8K FT TODAY AND DROP
TO AROUND 6K FT BY 12Z THURSDAY. NORTH FACING SLOPES OF THE HIGHER
ELEVATIONS MAY SEE 8-13 INCHES IN THE BEARTOOTHS, WITH THE BIG
HORNS SEEING 5-10 INCHES THROUGH THURSDAY EVENING. WE HAVE ISSUED
A WINTER STORM WARNING FOR THE BEARTOOTHS FROM 6 PM THIS EVENING
TO 6 PM THURSDAY...AND A WINTER WEATHER ADVISORY FOR THE BIG
HORNS/PRYORS FROM 3 AM TONIGHT THROUGH 9 PM THURSDAY EVENING. THE
BEARTOOTH HWY IS SCHEDULED TO OPEN FRIDAY BUT THERE MAY BE SOME
PLOWING NEEDED FIRST. WE COULD SEE SOME WET SNOW DEVELOP IN RED
LODGE BY MORNING, BUT WE EXPECT ACCUMULATIONS TO REMAIN UNDER AN
INCH ON NATURAL SURFACES THERE WITH ROADS JUST WET OR A LITTLE
SLUSHY.
AS THE SYNOPTIC FORCING SHIFTS EAST THURSDAY THERE SHOULD BE
ENOUGH INSTABILITY FOR THE DEVELOPMENT OF SCATTERED DIURNAL
SHOWERS ON THE BACK SIDE OF THE TROUGH (WHEATLAND/GOLDEN
VALLEY/STILLWATER/SWEET GRASS)...AND SOME THUNDERSTORMS ARE
POSSIBLE THURSDAY AFTERNOON ACROSS THE MT/DAKOTA BORDERS IN THE
WARM SECTOR AHEAD OF THE MAIN TROUGH AXIS. PRECIP SHIFTS
EAST/SOUTHEAST BY LATE THURSDAY EVENING WITH THE TROUGH AXIS
PUSHING INTO THE DAKOTAS.
FRIDAY THROUGH THE WEEKEND WILL TREND WARMER AND BE MOSTLY DRY,
BUT THERE MAY BE SOME WEAK PERTURBATIONS ALOFT TO PRODUCE
ISOLATED DIURNAL CONVECTION, AT LEAST OVER THE MOUNTAINS. AFTER
TEMPS IN THE 40S AND 50S THURSDAY...LOOK FOR TEMPS BACK TO THE 60S
FRIDAY, 70S SATURDAY AND INTO THE 80S SUNDAY.
THE FIRST HALF OF NEXT WEEK WILL SEE THE NEXT PACIFIC TROUGH
BEGIN TO MOVE INLAND. ENSEMBLE AND CLUSTER ANALYSIS STILL SHOWS
HIGH SPREAD IN POTENTIAL SOLUTIONS, RANGING FROM AN OPEN WAVE
ACROSS THE NORTHERN ROCKIES TO A DEEP LOW FORMING OVER THE SW
CONUS...BUT OVERALL TREND SEEMS TO FAVOR THE LATTER. IF THIS IS
THE CASE, ITS A PATTERN THAT WOULD POSSIBLY ADVECT LOW LEVEL
MOISTURE INTO OUR REGION FROM THE GULF. FOR NOW, LOOK FOR A WARM
START TO THE NEXT WORK WEEK (80S) THEN MODEST COOLING AND AN
INCREASING CHANCE OF SHOWERS/T-STORMS EACH DAY. BT
AVIATION
SCATTERED SHOWERS WITH ISOLATED THUNDERSTORMS WILL MOVE THROUGH
THE REGION THIS AFTERNOON. BEHIND A COLD FRONT THIS AFTERNOON AND
EVENING, WINDS WILL BECOME NORTHWESTERLY WITH GUSTS 25-35 KTS
POSSIBLE. ADDITIONALLY, MVFR/IFR CONDITIONS WILL BECOME MORE
LIKELY AS LOWER CEILINGS PREVAIL THIS EVENING. MOUNTAIN
OBSCURATIONS ARE EXPECTED THIS EVENING THROUGH THE PERIOD. TS
PRELIMINARY POINT TEMP/POPS
THU FRI SAT SUN MON TUE WED
-----------------------------------------------------------
BIL 043/056 039/068 044/079 051/086 053/089 054/085 053/079
+9/T 10/U 00/U 01/U 01/U 12/T 33/T
LVM 035/053 031/066 039/076 045/081 048/083 048/077 045/071
+9/T 20/B 00/U 01/B 01/U 14/T 45/T
HDN 041/056 036/069 039/079 046/086 049/089 051/085 051/079
+9/R 20/U 00/U 00/U 00/U 11/B 32/T
MLS 043/058 039/069 041/078 048/086 051/089 056/088 055/082
67/R 30/B 00/U 00/U 00/U 11/N 23/T
4BQ 042/055 040/066 040/076 047/084 051/089 057/086 055/079
28/T 71/B 00/U 00/U 00/U 01/N 23/T
BHK 038/061 038/064 037/075 046/084 050/088 056/087 054/082
26/T 74/W 10/U 00/U 00/U 11/N 23/T
SHR 039/046 032/063 034/073 040/081 043/086 045/082 044/076
3+/R 50/B 01/U 00/U 00/U 12/T 34/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...WINTER STORM WARNING IN EFFECT UNTIL 6 PM MDT THURSDAY FOR
ZONE 67.
WINTER WEATHER ADVISORY IN EFFECT FROM 3 AM TO 9 PM MDT
THURSDAY FOR ZONE 171.
WY...WINTER WEATHER ADVISORY IN EFFECT FROM 3 AM TO 9 PM MDT
THURSDAY FOR ZONE 198.
WEATHER.GOV/BILLINGS
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